The present invention relates generally to well pipe racking systems for moving pipe stands between racked positions and the well bore. Specifically, the present invention relates to a pipe racking system of the type used to support the vertical load of a stand of pipe while the stand is being transferred to or from the racking area on an offshore drilling platform.
In the drilling of oil and gas wells at offshore locations, it is common practice to rack the stands of drill pipe when the drill string is being tripped, as when the bit at the lower end of the drill string is being changed. Since a stand of drill pipe may be ninety feet in length, mechanized systems are desirable in offshore locations in restraining and handling the pipe stands to compensate for movement of the derrick which may be cauased by pitching and rolling due to wave action.
The typical mechanized pipe handling system thus includes one or more racker arms and heads which are used to guide the pipe stands into and out of the racking area and to and from the rotary. In addition, some type of lifting mechanism is required to provide vertical lift so that the pipe stand can be maneuvered without dragging along the derrick floor. In one prior device, the lifting head was mounted for movement along a vertical track. A hydraulic cylinder located below the lifting head was used to provide lifting force. This device was suitable for smaller loads but could not handle the weight of larger diameter pipe or greater stand length.
In another prior design, a lifting head was mounted in a vertical track and the lifting head was connected by a wire rope which ran over the crown of the derrick to a hydraulic cylinder which provided lifting force. The vertical track did not rotate about the longitudinal axis of the track and the wire rope was guided by a roller at the top of the vertical track.
There has existed a need for a beam type racking system of the type having a vertical track with a lifting head mounted on the track and connected by a wire rope to a source of lifting power, which lifting head was capable of X, Y, and Z movement with respect to the axis of the vertical track as well as rotational movement about the vertical track axis. Once the lifting head is made rotatable with respect to the vertical track axis, the need exists for a wire rope guide to constrain the wire rope and prevent undue wear or entanglement of the wire rope with respect to the other components of the pipe racking system.